[Python] concat_tables silently ignores unrecognised keyword arguments, including unify_schemas

### Describe the bug, including details regarding any error messages, version, and platform.

`pa.concat_tables` accepts `**kwargs` but only ever inspects `promote`. Every other keyword is dropped without a warning or an error:

```python
>>> import pyarrow as pa
>>> t1 = pa.Table.from_pydict({'a': [1.0]})
>>> t2 = pa.Table.from_pydict({'a': [2.0]})
>>> pa.concat_tables([t1, t2], totally_bogus_kwarg=123).num_rows
2
```

https://github.com/apache/arrow/blob/515410b2a1/python/pyarrow/table.pxi#L6324-L6338

Two ways this bites:

1. A typo in a keyword is silently ignored rather than raising `TypeError`, which is what a reader would expect from a normal Python signature.
2. `unify_schemas` in particular looks like it should work. It is a real field on the underlying `ConcatenateTablesOptions`, R's `concat_tables()` takes a `unify_schemas` argument, and the C++ option is what `promote_options` sets on the caller's behalf. So this reads as if it silently does the opposite of what was asked:

```python
>>> pa.concat_tables(
... [pa.Table.from_pydict({'a': [1]}), pa.Table.from_pydict({'a': [1.0]})],
... unify_schemas=False, promote_options="permissive").schema.field('a').type
DataType(double)
```

Schemas were unified despite `unify_schemas=False`.

This surfaced in GH-38809, where the reporter passed `unify_schemas=True` and reasonably assumed it had an effect. The type-promotion half of that issue is fixed; this half is not.

A fix could be either to raise `TypeError` on unrecognised keywords, keeping `**kwargs` only for the deprecated `promote`, or to retire `promote` altogether (it has warned `FutureWarning` since 14.0.0) and give `concat_tables` an explicit signature with no `**kwargs`. The second is a breaking change and would need its own deprecation window; the first is not.

Reproduced on pyarrow 25.0.1, macOS/arm64, and the code path is unchanged on `main`.

### Component(s)

Python